Electrical cut-out.



E. G. GILSON.

ELECTRICAL JUT-OUT.

AI'I'LIHA'IHJN 1'|1.1;nr1:n.1,1912.

Patented Dec. 22,1911.

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Canta/ns Lead Contains Graph/fa Engsten Shel/ac Contams Lead Inventor:

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UNITED STATES PATENT onric.

EMERY e. GILSON', or sc'iiENEo'rAnY, new YORK, ASSIGNOR TO GENERAL ELECTRIC com any, A eoaroiaarion on NEW YORK.

ELECTRICAL our-our.

Specification of Letters Patent.

Patented Dec. 22, 1914.

- Application filed February I, 1912. Serial No. 674,835.

To all whom it may concern Be it known that I, EMERY G. GILsoN, a citizen of the 'United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvementsin Electrical Cut-Outs, of which the following is a specification.

My invention relates to that class of safety devices known as cut-outs which depend upon the breakdown of a normally 1nsul .at" ing element forthe purpose of completing the electrical circuit.

My invention comprises both a new composition having an electrical resistance which may be varied to break down at a predetermined voltage and it also comprises a novel cut-out unit.

As an example of a device to which my invention applies I may refer to Patent N 0. 717,201 to J. W. Howell. In the type of cut-out described in this patent a sheet of insulating material is held between two metallic plates which are commonly arranged in shunt to devices connected in series, such as are or incandescent lamps. When one of these series devices fails to operate the insulating layer in the cut-out is punctured by the high'voltage across its terminals thereby completing the circuit and supplying current to the remaining devices. tant that the point at which the resistance of insulated layer breaks down shall be within limits which leave a safe margin above the normal operating voltage of the series device and which will be below the full line .voltage.

One of the main ob ects of my invention is toaprovide a cut-out unit in which the breakdown of the resistance will always take place within the assigned limits. I

I have found that a suitable insulating film having the above properties can be made by painting an absorbent fabric such as filter'paper with a composition consisting of finely divided carbon preferably in the form of graphite, a very finely divided powder of a metal of the tungsten group and a hinder or agglutinant such as shellac. The fabric thus impregnated is used preferably between metal contacts consisting of lead, or one of its alloys.

In the accompanying drawing Figure 1 is a cross-section of one form of a suitable apparatus in which the cut-out may be used, and Fig. 2 is a cross-section on an enlarged It is impor- The relative proportions of the ingredients of the insulating composition will vary with the break-down voltage required of the cut-out. An increased amount of graphite will increase the conductivity of the composition but I find however that the graphite content cannot be increased beyond certain limits without introducing irregularities in the break-down characteristic. The best results are obtained by varying both the graphite and the metal content. The tungsten or equivalent metal powder has some obscure efiect upon the binder, acting to lower its normally high resistance. lVith a given amount of binder a certain amount of metal is necessary but within certain limits an increase of metal content does not appreciably affect the conductivity. The proportions are governed by the conditions for which the composition is to beused. As a rule, the content of carbon by weight is in excess of the other ingredients and preferably is equal to, or in excess of the combined weight of adhesive material and metal. The adhesive material and the metal are usedin nearly equal proportion. As a specific example, I may state that for films which are intended to break down at a voltage varying between seventy-five volts and two hundred volts, I prefer to use a composition consisting of 112 grams finely divided graphite, 54. grams very fine tungsten powder and 54 grams of shellac. This mixture is thinned with 750 cc. alcohol, or other suitable solvent. This composition may be used in any convenient way in sheets, films, cartridges or sticks, but is preferably painted on one side of absorbent paper such as ordinary filter paper. The composition is simply rubbed in until a sheet is produced in a section of which the proportion of the high resistance composition is graded there being a thin layer of cellulose fiber free from composition on one side and the proportion of composition increasing as the other side isapproached. The sheet is then dried.

I find that the best results are obtained when disks of this insulating fabric are held between plates of metal which are not readily oxidizable and whichdo not give undesirable electrical effects when in contact with carbon. For example, the metal aluminum although not readily oxidizable will giveerratic results on direct current, probably due to a polarization action. After having tried a large number of metals '1 find that the best results may be obtained by using plates made of lead or an alloy consisting largely of lead and small amounts of some other metal such as tin which will harden the lead. I prefer an alloy. consisting of. 95 parts lead and .5 parts tin, although I do notwish to be limited to this particular alloy.

- The cut-out unit is prepared by arranging disks of the above described prepared fabric with a metal disk on each side. The paper disk Land metal disks 2, 3, Fig. 2, may be assembled to form a complete unit by pressing them together under a slight pressure at a temperature of about 170 to Cut-outs thus as- 180 degrees centigrade. sembled may be used as described in Howell Patent No. 717,201.

In Fig. 1 the cut-out 4 is shown as interposed between two flexible strips 8, 9, c0nnected to the terminals of a lamp socket 7 and adapted to be inserted between two spring tongues 5, 6, mounted on a fixed base 10 on which the circuit .connections are made at the terminals 11, 12; With this construction the lamp and its socket may be withdrawn from the base and the cut-out inserted between the springs 8, 9 and the lamp,

So long as the lamp is acting properly the film remains intact,

reinserted in the base.

but if the lamp should burn out the film resistance is broken down and connection is made between the springs 8, 9, thereby completing the line circuit independent of the lamp.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. A. cut-out device containing an absorbent material containing shellac, graphite and a finely divided powder of a metal of the tungsten group.

2. A film cut-out consistingofa cellulose fabric coated on one side with a composition containing graphite, tungsten and a binder, said composition. penetrating all but a thin layer of said fabric.

3. A cut-out device comprising metallic plates consisting largely of lead and an interposed layer containing graphite, ametal of the tungsten group and a binder.

4. A cut-out device comprising plates consisting largely of lead and an interposed absorbent paper impregnated with a mixture containing graphite, tungsten and shellac.

' 5. An electrical cut-out for series oonnected devices comprising plates of a lead-tin alloy, and an interposed paper coated on one side only with a mixture consisting largely of graphite, and containing also shellac and tungsten, said mixture penetrating all but a thin layer of the'paper. 7

In witness whereof, I have hereunto set my hand this 31st day of January 1912.

EMERY G. GILSON.

Witnesses:

BENJAMIN B. HULL,

HELEN Onronu. 

